Method and device for fault location of series-compensated transmission line

摘要

A transmission line system, a device for fault protection and computer programs, and a method for locating a fault in a series-compensated two-terminal power transmission line including a compensating bank for providing series-compensation to the transmission line. Different subroutines are utilized for locating faults on line segments from the first terminal to the compensating bank and line segments from the second terminal to the compensating bank. A selection is then made in order to determine a valid result. The subroutines utilize three phase currents synchronized measurements from both terminals and a three phase voltage measurements from one terminal for determining the respective per unit distance to a fault.

主权项

1. A method for locating a fault in a series-compensated two-terminal power transmission line having a length l and comprising a first terminal A and a second terminal B, and further comprising a fault locator and a compensating bank for providing series-compensation to said transmission line, said compensating bank being located at a per unit distance dSC from said terminal A and at a per unit distance 1−dSC from said terminal B, wherein dSC and 1−dSC are per unit distances of the length l, the method comprising the steps of:
determining, at the fault locator arranged in a differential relay that is incorporated into said transmission line, by means of a first subroutine (SUB_A), a per unit distance dFA to a fault (FA) occurring on a transmission line segment (LS1) between said terminal A and said compensating bank, said line segment (LS1) having said per unit distance dSC, wherein said per unit distance dFA is related to dscl, further relating said per unit distance dFA to said transmission line length l by
dA=dFA·dSC  (eq. 1), determining, at the fault locator by means of a second subroutine (SUB_B), a per unit distance dFB to a fault (FB) occurring on a transmission line segment (LS2) between said terminal B and said compensating bank, said line segment (LS2) having said per unit distance 1−dSC, wherein said per unit distance dFB is related to ((1−dsc)l), further relating said per unit distance dFB to said transmission line length l by
dB=dFB·(1−dSC)  (eq. 2), locating said fault by selecting, among the result dFA obtained from said first subroutine (SUB_A) and the result dFB obtained from said second subroutine (SUB_B), the result deemed valid, and calculating said respective per unit distance dFA, dFB to a fault (FA, FB), at the fault locator via said first and second subroutines (SUB_A, SUB_B), by utilizing three phase currents synchronized measurements from both terminals (A, B) and a three phase voltage measurements from one terminal (A) received by the fault locator from one or more measurement instruments measuring said transmission line,wherein said first subroutine (SUB_A) performs the steps of:
determining symmetrical current and voltage components (IA1, IA2, IA0, IB1, IB2, IB0, VA1, VA2, VA0,) corresponding to said three phase currents synchronized measurements and to said three phase voltage measurements, determining a fault loop voltage (VAp) as seen from terminal A based on said corresponding symmetrical voltage components (VA1, VA2, VA0) and based on type of fault, determining a fault loop current (IAp) as seen from terminal A based on said corresponding symmetrical current components (IA1, IA2, IA0) and based on type of fault, determining a total fault current (IFA) by using a generalized fault model:
IFA=aF1IFA1+aF2IFA2+aF0IFA0  (eq. 6),wherein aF1, aF2, aF0 are coefficients related to type of fault and wherein IFAi is determined as a sum of the ith sequence components of currents from both ends (A, X) of said line segment (LS1),
neglecting transmission line shunt capacitances, thus obtaining
IFai=IAi+IBi  (eq. 8) determining said per unit distance dFA based on said fault loop voltage (VAp), on said fault loop current (IAp) and on said total fault current (IFA), and wherein said per unit distance dFA is determined by solvingdFA=real⁡(V_Ap)·imag⁡(I_FA)-imag⁡(V_Ap)·real⁡(I_FA)real⁡(Z_1⁢⁢LA⁢I_Ap)·imag⁡(I_FA)-imag⁡(Z_1⁢⁢LA⁢I_Ap)·real⁡(I_FA).(eq.⁢10)